4_8.springboot2.x嵌入式servlet容器启动原理解析

问题描述:
什么时候创建嵌入式的Servlet容器工厂？
什么时候获取嵌入式的Servlet容器并启动Tomcat?

*获取嵌入式的Servlet容器工厂：

1）、SpringBoot应用启动运行run方法
2）、refreshContext(context);SpringBoot刷新IOC容器【创建IOC容器对象，并初始化容器，创建容器中的每一个组件】；如果是web应用创建AnnotationConfigServletWebServerApplicationContext，否则：AnnotationConfigApplicationContext

a、创建容器并且判断：

刷新容器：

3）、refresh(context);刷新刚才创建好的ioc容器；

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

4）、 onRefresh(); web的ioc容器重写了onRefresh方法
5）、webioc容器会创建嵌入式的Servlet容器；** createWebServer();
6）、获取嵌入式的Servlet容器工厂
ServletWebServerFactory factory = getWebServerFactory();
从ioc容器中获取ServletWebServerFactory**组件；
tomcatServletWebServerFactory创建对象，后置处理器一看是这个对象，就获取所有的定制器来先定制Servlet容器的相关配置；
7）、使用容器工厂获取嵌入式的Servlet容器：
this.webServer = factory.getWebServer(getSelfInitializer());
8）、嵌入式的Servlet容器创建对象并启动Servlet容器；

先启动嵌入式的Servlet容器，再将ioc容器中剩下没有创建出的对象获取出来；

IOC容器启动创建嵌入式的Servlet容器